Reflector lamp



1,624,762 April f 1927' A. RUTTENAUER ET REFLECTOR LAMP Filed May 1926 --In\/entc r5 Alfred Riittenauen Georg Gem-dies. b W

Their Abbcprn ey.

Patented Apr. .12, 1927.

UNITED STATES PATENT OFFICE.

ALFRED nfir'rnmr'unn, or CHARLOTTENBURG, BERLIN, AND GEORG Gmm's, or ran- KOW, BERLIN; GERMANY, ASSIGNORS PORATION OF NEW.YORK.

TO. GENERAL ELECTRIC COMPANYQA COR- REFLECTOR DAMP.

Application filed May 14, 1926, Serial No. 108,160, and in Germany June 26, 1925.

In clectricincandesccnt lamps attempts have been made to utilize a portion of the bulb .of the lamp as a reflector by applying to it a thin silver coating'to make the lamp a Searchlight. This simple and advantageous method for securing a directed beam of light can not be used in lamps in which the bulbs, on account oftheir small size-or the use of a high wattage filament, heat upto 10 more than 250 degrees C. for example, be-

cause the means which have been proposed to protect the silver coating against oxidation do not withstand such high heating of the bulb for any length of time. For example, aluminum bronze, frequently used as a protective coating for the" silver, will withstand temperatures of the bulb of only about 150 degrees C. for at even lower temperature the aluminum bronze layer swells and finally scales off. The many lacs proposed for the protection of the silver coating are as a whole not essentially more heat resistant than any aluminum bronze layer. The aquadag layer sometimes used in reflector automobile lamps and made from a colloidal carbon solution does stand somewhat higher temperatures, but at temperatures of about 0 degrees C. is on the point of vaporizing, so that in automobile lamps of high candle power a coating of the in-' terior of the automobile headlight by vaporization of the protective layer cannot be avoided. Even when the silver coating is covered on the outside with nickel with the interposition of a copper coating the bulb temperature must not exceed approximately 200 degrees C. or at most 250 degrees C. as otherw se damage orflaking off of the outer nickel protective layer takes place. Such a protective layer also has the further disadvantage that if a very fine hole or fissure in the outer nickel layer is present or de-, velops, yellow spots are produced on the silver 111111'01 by the oxidation of the copper. It has also been proposed to protect the silver coating by a ceramic coating consisting of a mass of very hard silicate. This coating, though it-is highly refractory, has the disadvantage that it is porous and allows especially at high temperatures, the oxygen of the air tmseep through to the silver coating, causing discoloration or spotting of the silver coating. A further disadvantage of this hard ceramic protective coating is that enamel layer fused over it.

it can be made only ina comparatively thick and irregular layer, which naturally makes the lamp" unnecessarily heavy and detracts from its appearance: I

This invention provides a means of so prute'ctin a silver coating on the bulb of an electric lamp that the bulbfcan, in operation,

be raised, without danger to the coating, to

far higher temperatures, even above'400 degrees C. To this end, thethin silver layer employed for the reflector is protected by an The enamel layer, by t e fusionof its particles produced during the application of the layer, attainsa smooth surface which: hermetically seals oil the silver coating from the outside, so that even with a higher heating of the bulb than has heretofore been feasible, the en-- trance of airto the silver coating becomes impossible. The smooth; surface of this protective layer and the fact that it can easily be made of very slight thickness has as the further advantage that the lamp is not impaired in its appearance and has only a. slightly greater Weight than an'ordinary silver coated lamp.

In the accompanying drawing we have illustrated as one example of a lamp embodying our invention, an automobile lamp of which Fig. 1 is an elevation and Fig. 2 a section through a part of the coated part of the bulb. In thisparticular lamp the glass bulb 1 has on a portion of its surface a refleeting layer or coating 2 of some metal, such as, silver, covered with a smooth protective layer 3 of enamel fused in place over the. silver reflector to hermetically seal the silver coating from the air. As a result, the reflector is protected from the action of the air even though the bulb attains a temperature as high as 400 degrees In the'manufacture of a lamp in accordance with our-invention, the following process can be followed:

The lamp bulb 1 or evena completely finished lamp. is first carefully cleaned and thendipped' for some minutes into one or. several silver plating baths to apply the silver coating and then allowed to dry. Then the bulb or lamp is put into a bath of an enamel in suspension and preferably containing some clouding means dissolved in alcohol, or else the suspension is applied to the bulb by squirting, pouring or painting.

It is also possible to apply the enamel by dusting on a dry, easily fusible enamel ,p owder. heated in-a furnace or b gas burners for some minutes to the burning in temperature of the enamel, whereupon the separate particles. of the enamel are fused and form a smooih, uniform surface even when the enamel is in a very thin layer. In order to avoid deformation of the lamp bulb when theenamel is burned in, there must naturally be chosen an enamel which is suitablefor the'bulb glass. If the lamp bulb consists, for example, of'hard glass. such as a diflicul-tly fusible magnesiaor b oro silicate glass, then most of the enamels on the market can 'bedirectiy applied. If, however, the lamp 'bulb consists of the ordinary lead glass with a melting point of 500 to 550 degrees 0.,

then it is preferable to use an enamel havmg a burning in temperature which does not exceed 4180 degrees The la'mpsprovided with. the new enamel protective layer can-perman'ently stand tem peratures of'more than 400 degrees C. without damage 'or'changes in thecons'i'stency of the protective layer or ofthe underlying silver coating. As a result, the invention can "advantageously be employed wherever a good concentration is desired of the light of a lamp which in'operation reaches a high heat, such as projection lamps, automobile lamps, and searchlight lamps. It is immaterial whether the lamp is a vacuum incandes- The applied enamel layer is finally cent lamp, a gas filled incandescent lamp, or an arc lamp having a bulb.

While We have described as one embodi- 'ment of our inventiona lamp having abulb of which a portion is made into a reflector by a coating of silver, our invention is not l-OStl'lCtCd 10 such embodiment, but is ap- 2. A reflector comprising .a sheet of glass and a coating of highly reflecting metal susceptible to oxidation at high temperature adherent to the glass and hermetically sealed from the air by a protective layer of fused enamel. V

3. A reflector comprising a curved sheet of glass and a coating of-silver on its surface protected by an air tight smooth layer of plicable to searchlight and similav reflectors enamelfused in place on .the glass and over said coating. In witness whereof, we havehereunto set our hands this 27th day of April, 1926. ALFRED RUTTENAUER. GEORG GAIDIES. 

